Btu Calculator
Calculate BTU requirements for heating and cooling systems. Free, fast, accurate — no signup, mobile-friendly, works in
Calculation Type
Room Dimensions
Room Area:300 sq ft
Room Volume:2,400 cu ft
Environmental Factors
BTU Basics
BTU: British Thermal Unit - energy to heat 1 lb water by 1°F
Cooling: ~20 BTU per sq ft (basic rule of thumb)
Heating: ~40-50 BTU per sq ft in cold climates
1 Ton: 12,000 BTU/hr cooling capacity
Calculation: Cooling Load Calculation
Required BTU
12,714 BTU/hr
Calculated heat load
Recommended Capacity
13,985 BTU/hr
With 10% safety margin
System Tonnage
1.2 tons
AC/Heat pump size
Power Equivalent
3,724 watts
Electrical equivalent
System Size
Small (1-1.5 ton)
Recommended system category
Daily Cost
$10.73
Est. energy cost
Monthly Cost
$321.76
Est. energy cost
Annual Cost
$3,914.75
Est. energy cost
How it works
A BTU calculator estimates the heating or cooling capacity a room needs. The British Thermal Unit measures heat energy; for air conditioning, a rough rule is about 20 BTU per hour per square foot of floor area, adjusted for sun, ceiling height, and occupancy.
Cooling capacity
BTU/hr ≈ area (ft²) × 20 (adjust for sun, ceilings, people)
- area
- room floor area in square feet
- 20
- base BTU per ft² (raise for sunny/tall rooms)
Worked example
- Room = 300 sq ft
- Average sun and ceiling height
- BTU = 300 × 20
≈ 6,000 BTU/hr of cooling needed.
Good to know
- Add ~10% for very sunny rooms and ~4,000 BTU for a kitchen; subtract ~10% for heavily shaded rooms.
- Oversizing an AC makes it short-cycle, cooling without removing humidity.
- Add ~600 BTU for each person who regularly occupies the room.